Heat treating furnace



III E1... E1

Jan. 21, 1958 H. E. MESCHER 2,820,622

HEAT TREATING FURNACE Filed Feb. 21, '1955 s Sheets-Sheet 2 M42020 1:. MescHe-e INVE/W'GE ATTOEMEY Jan. 21, 1958 H. E. MESCHER 2,820,622

HEAT TREATING FURNACE Filed Feb. 21, 1955 3 Sheets-Sheet a HA R040 8 M55 CHE'E l/VVE/VTORS ff/K Annex/Ev United States Patent U HEAT TREATING FURNACE Harold E. Mescher, Rivera, Califl, assignor to Pacific Scientific Company, San Francisco, Calif., a corporation of California Application February 21, 1955, Serial No. 489,595

6 Claims. (Cl. 263-21) This invention relates generally to heat treating furnaces, and the invention has reference more particularly to a novel shaker-hearth-type heat treating furnace.

In shaker hearth furnaces, the work to be heat treated is fed on to a reciprocating hearth, which, through its motion, serves to automatically move the work or parts treated through the furnace. In furnaces of this type as heretofore constructed, it has been diflicult to keep the hearth from warping while the work is being fed thereover due to unequal expansion and contraction of dificrout parts of the hearth, the portions of the hearth covered by the relatively cold work or pieces entering the furnace being retained in a relatively cool condition whereas the portions of the hearth not so covered tend to expand owing to the heat of the furnace, thereby causing the hearth to buckle or bulge upwardly making it diflicult to maintain a minimum door opening, resulting in an undesired oxidation of the work parts as they pass through the furnace, and also reducing the rate of speed at which the work can be fed through the furnace due to undesired ingress of cold air.

Although the hearth is thus buckled upwardly in the area consisting of the first three or four feet of the hearth within the mufile while work is passing through the furnace, necessitating an unduly wide door opening, this portion of the hearth will assume a flat position between work cycles, i. e., when the work has passed off this part of the hearth and the same becomes uniformly heated and returns to its normal level position. This constant bending and unbending of the hearth results in failure of the sidewalls of the hearth within a relatively short time, due to the formation of cracks which creep all the way across the hearth making the unit inoperative. Attempts have been made in the past to ofiset this difficulty by inserting a secondary hearth on top of the main hearth, but experience has shown that while such secondary hearth will protect the main hearth, it itself will fail due to buckling within a short time after being put into use.

After carefully studying the problem, I have found that the reason for the warping is the chilling elfects taking place on the floor of the hearth by the cold incoming parts, while the two sidewall upwardly extending retaining flanges of the hearth are maintained at oven temperatures. This condition causes the hearth to move upwardly due to the greater expansion of the flanges than that of the floor of the hearth, which upward movement may amount to two to four inches in the first three or four feet of the hearth within the furnace. Attempts also have been made in the past to employ a series of hearth segments or interconnected plates, which, while serving to prevent excessive heat from reaching the hearth itself, nevertheless make it extremely difiicult to employ a minimum door opening owing to the irregular contour of the segments or plates.

It is therefore the principal object of the present invention to provide a novel heat treating furnace of the shaker hearth type having a hearth construction that provides for a minimum door opening in operation, while at the same time ensuring long life of the hearth in use.

Another object of the present invention is to provide a novel heat treating furnace of the above character, so constructed and arranged as to enable easy movement of the work through the muffle of the furnace and having improved hearth actuating means.

These and other objects and advantages of the present invention will become apparent from a perusal of the following specification taken in connection with the accompanying drawings wherein:

Fig. 1 is a longitudinal sectional view in elevation of the novel furnace of this invention.

Fig. 2 is an enlarged fragmentary view of the front of the furnace of Fig. 1.

Fig. 3 is a plan view of that portion of the furnace hearth and associated parts which substantially project in front of the furnace, and Fig. 3(a) shows a portion of the hearth that is located inwardly of the furnace.

Fig. 4 is a view in side elevation of the structure of Fig. 3.

Fig. 5 is an enlarged view of a portion of the hearth designated by the lines 55 of Fig. 1.

Referring now more particularly to the drawings, the reference numeral 1 designates the shell or casing of the furnace which is internally lined with heat insulation 3 shown surrounding heating elements 39 adapted for heating a muflle or oven 2 contained within the furnace shell. Shown within the muffie 2 is the primary or main hearth 4 consisting of a longitudinally extending web or plate having upstanding continuous side flanges 4. The primary hearth 4 is supported for swinging forward and rearward movement by means of hangers 5 having the shape of rods with bent over upper ends supported upon transverse rods 6 extending across the muflle 2 within the same. The lower ends of the hangers 5 extend across the hearth 4 and beneath the same and support the hearth by means of angle bars 7 welded to the bottom of the hearth. Arcuate retaining plates 8 are welded at one side of an edge of the angle bars 7 and serve to retain the hanger rod 5 within the angle bar 7 while permitting relative turning movement of the hanger rod within the angle iron.

In order to actuate the hearth in use, the underside of the hearth near the forward end thereof is provided with a transverse shaft 9 welded thereto, which shaft extends beyond the sides of the hearth 4 and has its end portions turnably mounted in apertures provided in depending links 10 and 10', the upper ends of which links are turnably supported upon studs 11 carried by frame 12 of the furnace. The lower ends of the links 10 and 10' carry a follower shaft 13 on which is mounted a follower roller 14 for cooperating with a step cam 15 fixed upon a cam shaft 16 having its ends mounted in bearings 17 carried by the frame 12. One end of the cam shaft 16 has a sprocket 18 thereon driven by a sprocket chain 19 driven in turn by a motor 20.

The primary hearth 4 is urged inwardly of the furnace by coil springs 21 and 21 which are connected to brackets 22 fastened to the forward end of the hearth flanges 4 and also connected to washers 23 loosely fitting and adjustable along rods 24 fixed upon frame 12. Thus, in use, by adjusting the washers 23 along the rods 24, the relative tension of the springs can be varied to determine the rapidity of movement of the hearth 4 and the rate at which the work will feed over this hearth. As the motor 20 turns, the step cam 15, acting through the roller 14 and the follower shaft 13, will move the links 10 and 10' forwardly against the tension of springs 21 and 21, and hence move the hearth forwardly since these links are connected to the hearth via the transverse shaft 9. As the roller 14 rides off the step of the cam 15, the springs 21 and 21' will move I hea'nth-nearwardimzor ztowardstheisiettr asr-viewe t serving-toiurg'e t-he he'ai th sion, but also serving to retaiii th' hearth centered-ninth a the hearth .r'eatw ardly suddenly tnntil .theabumpersb1ock 25 on the hearth abuts the cushioned stop 26 carried by the frame 12. Thus, eachtirne as the springs move 1, the work thereon-:is'iadvanced into theifii'rna springs 21,5121" :ido nut zextend paraliel to the sieies of therih'earth-mebutiextenii mitwa 1y at equaliy inclined angles athereto; :sh'own thereby "not ear aware wiihehe fies'iretit'en th'a't may beraised of'lowere d with respect to the hearth 4 to vary the input opening "ofthe' ni'uifie. fin ofdertowrevent undesired oiiifiation" fiiffhe work within the furnace, iris-"desired thaf'the iovveredge' of "the doof-27be PGSifiOITB Ii HS 'ciose"to th'ef'top of the hearth 4 as practi'cablefand hehcefifi'sesseiitialthat'the hearth remain trulyhorizontal at an tinies iii use. "To'prevent the buckling of the hearth, the .same is provided With-a series of consecut'ive proteetive shingles or cover plates 28, 29, 30, 3'1, 32 3. These shinglesor protective "cover iaies 7 plate'f'and upstanding sine iia'nges and a e 't'e'lesco ecione intoanothe 'as shown l innhe tiravvin s, and serve to overlieithe upper surface (Sf the gp'rimarfhearth AIin heat'pro'te'ctin'grelation. "Thus; fsliingle..-28,"for vexample" (seelFigs. .3 and 1), is' providedwith side flanges-34 adjacent primary *hea'rth -flanges i llaiand this shin g le is made narrower atits rear end than at its forwardend, so 'thafits rear end wiilgprojecteon ewhatiinto the :for- Ward and wider end of .sliingIe -ZQ, in overlapping; rela- 'tion, as .especiallyfshown inFig. 3,thereby providing a wedge-shaped Insulating-dead lair vspace ..betwe en-.the shingle and the .main hearth 4. The forward endaedges V of the shingles are-Weldedialong their fiattrbotto'rns, :as

permit :varying telescoping: movement to compensatei-for temperature changes:an'ci alsoiaidfin movingi'the work rearwardlyrin the furnace.

prevent heat from iescapingironi'i-the main hearth-Jto 'the shingles 'an'd thence'tozthe-cold incoming work.

These shingles iori'pl'ates cover the m'ain or primary hearth 4 in that region within the muflie where 'the'work isI-introduced, i. e., 'the -f'orward' portion of the mufile, and 'where the work'iis necessatily cold. -.S'u;h shingles formingithe :w'edge-Ishaped deadxair s'pa ces thereunder prevent undue thermal expansion 'andcontraction of the forward'portion of the' rfiain hearth since they thus-t ly :protect ;this -portion of the hearth -'against thezchilling veifect o'f the -nevvly :entering work, so that the main hearthisxuniformly ihe'a't'ed b'y the furnace 'at 'all times and retains iitsplane :trn'iy h'ori'zorital shape, enabling the door 2710 have :a minimum openin at all times during the operation of: the -furnace, thereby Lk'eeping out undesired'air and' retaining roper:atmospheric conditions within vthe i'n'u'file 2; This-desired atmospheric condition is further enhanced by *use "of a gas flamesupplied by the burner' 36 located below the 'dooril. By the 'time the *woikthas ie'ft the lastshiugle '33. itihas reached The iinsulating wedge-shaped dead air spaces between ithe shinglestandthe 'm'a'in hearth the temperature of vthe. furnace,and hence it does not cause any warping or distortion of the rear portion of V the main hearth 4a Since the shingles telescope one within the other, they are free to expand and contract by the telescoping action without stress being set up in the shingles, so that thesnovel hearth of this invention has an extremely long li'fe in "use. The heated work leaving the enti -.of;th'e..mainihearth is s'hown dropping into a quench tank 37. The rear end of the mu-ffie is shown Elmediby awear removahie iu' is's havin a vent 39" and thermocouple control 10. v}

Since many changes could be made in the above construetioii of the "furnace-and i'n'any apparentlyzwidely different embodiments-sot this invention could be made without departing -from the scope thereof, it is intended that all matter contained in the description or shown in the accompanying drawings shall be interpreted as illustrative"and not-in admitting sen'se.

Whatiscla'imed-is i i n V l. A heet treating ifu'r-nztzetompris'ing a mufileya shaken hear th extendin'g longitudinally-withinsaid mufile e-fo'rhied with a hat bottom v and being mounted for 'r'eeipto'catin'g "movement therewithin-said shake bean-h comprisi g amainhearth wet; i lui'a lity ot ccessive shingles carried ,by"said ma'in hearth web,--eaeh of said shingles being "afiixed at one 'enii only 'to "said "m'ai'ri hea'ith web "and overlapping dj hing-shingle a't its-"other end for -rel-at-ive telescoping movementwith said adjoining -'shingle,'*thereby to eonipensate for therniaI expansion and'contraction of the shingles without?[melding-thereonthe verlappi g-of said shingles" providing consecutivefdead air s aces: betwee'" said *main' hearth"-and*said-shihgles for preventing 1 the- 'ehiiling of vsaid main -heart h hy'eolii work assing over said shingles thereby'preventing buckling of said main hearth. H

2. 'Ai futhac e of the character tleserib'ed;"compiisinga casing, a mufii'e I Within-said "casin anii "insulated therefrom, a shaker hearth Within said muflie and extending respect to'said mufile,-'said spring means comprising a longitudinallyhthereof, 'hangers':suppor'tin'g said shaker hearth for longitudinal oscillatorymovementwithin. said mu'file said shakerhearth comprising a maini'web' having consecutive 'ov'e'rla'pping shingles, said shingles providing wedge-shaped dead 'air spaces between *thes'a'meand said main we b fo'r heat insulating-the latter, motor means connectedfo'r moving saidhearthin'termittently'forwardly with'respect to 'said muflle, and'spring m'eans connected for urging 'sai'd hearth "interm'i'tten'tly''re'arwartllywvith :pair ofrsprings eonnected to the""forward endof'fsaid hearth and extending-"rearwardly and outwardly ffoi-ais'o centering saidhearth vvithinsaidrmuiiie while atfthe same time-ur ing -the he-aith' rearwardly against the-action or :saia motive means'tor inoving th'e wo'rk rearwardly within 3. A furnace as' defined zincl'aim" 2 wherein the'saiti shaker hearth main hearth w'eb "extends longitudinally tain a said mains-hearth: at uniform temperature, preventing V .thei-bucklingzand distortion of the same iinluse; the rearward ends 10f vsaidv shingles by their "telescoping action permittingthernral expansion and :contraction vthereof withouteanyxbuckling iof theishingles while at the-same time, :the rear edges :of said-shingles faid in =moving the work rearwardly.

4.J A.4 hea't ..treatin gi furnace comprising Ian elongated.

casing, a mfih'le: extending longitudinally within .s'aideicas- .ing and insulated therefrom, ;means -inte ;posed between said imifiieand its 'insulaiioniorlhe'afing;saidmuflie and contents; 'a shaker hearth having a hat 'bot'tom plateianfi siiieflanges extending longitudinally within said muifi and projecting outwardly through the forward open end thereof, spaced hangers for pivotally supporting said shaker hearth within said mufifle, protective non-buckling shingle members overlying said hearth plate and providing dead air spaces between the hearth plate and the shingles for preventing work handled by said furnace from chilling said hearth plate and buckling the same, motor driven cam and follower means for intermittently moving said hearth forwardly within said muffle, and spring means for intermittently moving said hearth rearwardly within said muffie to efiect movement of the work within said mufiie.

5. A heat treating furnace as defined in claim 4 wherein said spring means comprises tension springs connected to the forward sides of said hearth and extending rearwardly and outwardly of said hearth, and connected to said casing for also automatically centering said hearth within said muffle.

6. A heat treating furnace as defined in claim 4 wherein shingles overlying the forward portion of said hearth,

References Cited in the file of this patent UNITED STATES PATENTS 1,881,887 Normann Oct. 11, 1932 2,021,072 Machlet Nov. 12, 1935 2,380,452 Kohout July 31, 1945 2,662,635 Joy Dec. 15, 1953 OTHER REFERENCES Trinks Industrial Furnaces, Volume 1, third edition, copyright 1934, published by John Wiley and Sons, 111- corporated, New York, N. Y., pages 287 and 288. 

